When shipping goods to construction sites, especially large loads such as bundled building trusses, there are unloading problems. If a special "cradle" truss trailer or a conventional flatbed trailer is sued, on-site equipment such as a crane or forklift must be available to unload the trailer. Because of scheduling difficulties, often such equipment is not ready when the trailer and its load arrives at the site. The equipment needed to unload the trailer may be busy with other more urgent tasks or it may not have yet arrived at the site itself. In such circumstances, the truck driver has to choose between waiting (perhaps for hours) for the equipment to unload his trailer to be available or going about other tasks and returning later.
In either case, the result is a costly loss of equipment use time and driver time.
To overcome this problem, it has been proposed to make trailers with a bed of rollers and to unload by untying the load and "jerking" the trailer forward and, hopefully, rolling and dropping the load on the ground off the rear of the trailer. However, this involves subjecting the load to a drop of at least two feet off the tail or back edge of the trailer. While some loads can take such abuse, others are damaged in the process.
Tilting trailer beds have been successfully used with drive-off equipment. U.S. Pat. Nos. 4,125,198; 2,717,707; 4,568,235; and 2,717,707 are examples of such trailers. Such trailers are not well suited for unloading loads which cannot be driven off of the trailer. A similar principle has been used for unloading containers. For example, U.S. Pat. Nos. 3,934,740 and 3,606,059. However, all such tilting-bed trailers require extra power units, such as hydraulic rams and often a winch. The latter two examples also require specialized containers which must be unloaded and picked up later. Thus, these are not suitable for use in unloading a "one-way" item such as a bundle of building trusses. Such prior trailers also require special articulated pivoting sections and special controls to operate the power units so as to articulate the various sections. These controls, extra power units, and articulated sections increase the initial cost and complexity of the trailer, require special tractors or power mover units, and are prone to wear and break down, with the consequential increase in maintenance costs and down-time.